Modern automotive automatic transmissions are produced with an internal pump for supplying hydraulic fluid at selected pressures for operation of the various components within the transmission that relate to gear shifting. Such internal pumps operate only when the vehicle engine is operating. For this reason, a vehicle supplied with a modern automatic transmission cannot be push or pull started.
Further, a modern automatic transmission cannot be relied upon to slow the associated vehicle using engine compression without the engine running. Once the vehicle slows to a point where the internal pump is not working, the transmission will shift to a non-operational mode and allow the vehicle to freewheel. This can be a dangerous situation especially if the vehicle is equipped with power steering and brakes, since the non-running engine will not provide operational power to drive the power steering or power brake pumps. Vehicle handling thus becomes dangerously difficult.
Actually, the above problems were answered to a limited degree in many automatic transmissions built prior to 1966. Many of these previous transmissions included internal secondary pumps that were driven by the vehicle drive lines, not the engines. This type of transmission had the advantage of allowing push starts once the vehicle was pushed beyond a speed where the secondary pump (being driven by the vehicle drive line) would build sufficient hydraulic pressure to operate the transmission. This usually required speeds of 15-30 mph. The transmission could also be counted upon to slow the vehicle (by selection of lower gears) to lower speeds than modern transmissions. However, the transmission could only slow the vehicle while the secondary pump remained operable.
Even with the above advantages, the secondary pumps added to the overall manufacturing costs for the transmissions. The secondary pumps themselves were not without drawbacks. In addition to the cost factor, such internal pumps required periodic maintenance and replacement, since they operated continuously while the vehicle was moving (even when use was not required). Maintenance or replacement of the pumps was difficult and costly to the vehicle owners. Additionally, the required speed for push or pull starting often led to dangerous situations. Still further, the pumps were not switchable and since they were operational at nearly all times the vehicle was in motion, an unnecessary reduction in fuel efficiency was experienced (it took energy to run the pumps even when they were not needed for transmission operation).
The present invention provides solutions to problems found with both forms of transmissions (those with primary pumps only, and those with primary and secondary pumps).
The present invention provides an auxiliary fluid pressure source that is provided outside the standard automatic transmission housing and is connected to the pressure lines within the transmission in order to selectively deliver operating fluid pressure to the internal working components of the transmission. By doing this, pressure may be supplied to the transmission regardless of inoperability of the engine, primary or secondary pumps, so the transmission will remain operational as long as the auxiliary pressure system operates. Since the pressure system may be operated by energy supplied independently of the engine and drive line, there is no requirement that the vehicle be moving at speeds sufficient to elevate the fluid pressure to operational levels, or that the engine be operating for the transmission to be operated.
An object of the invention is thus to provide an auxiliary pressure system for automatic automotive transmissions that may be operated independently of drive line operation or internal transmission pump operation.
A further object is to provide a pressurization system that may be produced along with transmissions or that can be added as a retrofit to existing transmissions.
A still further object is to provide such a system that may be operated to enable low speed push, pull or inertia starting of a vehicle engine.
An additional object is to provide such a system that may be operated to enable use of an automatic transmission to effectively slow a vehicle using engine compression braking to low speeds without the engine running, and thereby permitting operation of associated power steering and power brake pumps to enable safe handling of the vehicle.
The above and still further objects and advantages may be realized from the following detailed description of the invention.